A material's broad susceptibility to fatigue fractures is only one factor affecting frame longevity. Others include the quality of the design and fabrication, the suitability of the particular alloy or version of the material for the task, the stress the material will be subject to, and corrosion.
Don't necessarily rule out aluminum. Birdys have an aluminum frame but are extremely long lived. The suspension protects the frame from high peak stresses when you hit a bump, the design and fabrication standards are very good and they are designed to eliminate the potential weak point of a hinge in the main frame.
There are examples of good designs that can be expected to last a long time in both steel and aluminium.
David
PS. Re: repairs in remote locations if that is a concern.
Your best defence is not to need them. The best and lightest steel frames use thin heat-treated steel alloy tubes and re-welding them successfuly in remote locations without creating a weak point may be as problematic as with aluminum.